356 THE BACTERIOPHAGE AND ITS BEHAVIOR 



RESUME 



All of the arguments which have been advanced by the adherents of 

 the diverse hypotheses concerning the nature of the bacteriophage cor- 

 puscle are indirect arguments, that is to say, arguments which tend 

 only to show that such and such a fact "fits in better," ''explains better" 

 such and such an hypothesis. Such arguments are valid only through 

 interpretation, and each may be interpreted according to the taste of 

 the individual; it is purely a question of dialectics. 



Logically, a demonstration must be based on direct arguments, that 

 is, on arguments which are not subject to interpretation, arguments 

 which inherently exclude all hypotheses other than the one which they 

 support. In this way only can an hypothesis be transformed into a 

 certainty. 



The question as to the nature of the bacteriophage corpuscle can be 

 asked in but a single way: Is there a group of characters, constituting 

 the "criterion of life" which permit us to place the being in question 

 irrevocably either in the category of living beings or in the category of 

 inert beings, depending upon whether it possesses or does not possess 

 this combination of characters? 



If this criterion exists, does the bacteriophage corpuscle conform to 

 it, or does it not? 



The criterion of life exists. It is formed of a combination of the 

 powers of assimilation in a heterologous medium and of adaptation, 

 with their corollaries, the faculty of multiplication and the capacity for 

 variability of characters. 



Experiment demonstrates that the bacteriophage is an autonomous 

 being, independent of the bacterium at the expense of which it multi- 

 plies. By virtue of the fact that this autonomous being multiplies 

 at the expense of the bacterium, heterologous with respect to itself, 

 it must necessarily transform a heterologous substance into a homolo- 

 gous substance, a substance distinctively its own substance, and conse- 

 quently it is endowed with the power of assimilation. 



Various experiments show that the bacteriophage corpuscle is able 

 to adapt itself to adverse conditions. The corpuscles therefore possess 

 the faculties of reproduction and of variability. 



The bacteriophage corpuscle possesses, therefore, precisely that com- 

 bination of characters which permit us to recognize that a being is liv- 

 ing, and anything which possesses the criteria of life is necessarily living. 



The living nature of the bacteriophage being estabhshed, all facts 



